The tool "allows us to compare human demands on nature with nature's ability to renew resources," said Mathis Wackernagel, co-creator of the tool and executive director of the Global Footprint Network in Oakland, California.

Today humanity's ecological footprint is nearly 30 percent larger than what the planet can regenerate in a given year, the tool reveals.

For example, forests are cut down faster than they regrow, fish are taken from the oceans faster than their populations regenerate, and groundwater is sucked up faster than aquifers are replenished.

To better manage our resources, world leaders should balance their ecological footprint the same way that they balance their finances, Wackernagel and colleagues say.

"If you don't look at your bank account statement, how do you know if you are moving toward bankruptcy or success?" Wackernagel said.

Going Bankrupt

Wackernagel and his then professor William Rees at the University of British Columbia in Vancouver, Canada, created the Ecological Footprint tool in the wake of the 1992 United Nations Earth Summit in Rio de Janeiro, Brazil.

Sustainability—living within the limits of the Earth's resources—was a buzzword at the time, Wackernagel says, but nobody knew what those limits were.

"If we don't look at the global limits and act accordingly, sustainable development is futile. It's totally futile," he said.